Belo owns 20 stations in major markets that also include Dallas/Fort Worth, Houston, Seattle, St. Louis, Portland, Ore., San Antonio, Austin, Texas, and Phoenix.

In Louisiana, the company owns WWL, the CBS station in New Orleans, and WUPL, a MyNetworkTV station in New Orleans, but licensed in Slidell.

Under the agreement announced Thursday, Gannett will pay $13.75 per share for the TV station operator, which is based in Dallas. That represents a 28 percent premium over Belo’s closing price on Wednesday.

Gannett, the largest U.S. newspaper publisher by circulation, also will assume $715 million in debt. Gannett owns USA Today and other newspapers as well as television stations.

If approved, the Belo deal will make Gannett the fourth-largest broadcast group in the U.S.

The Federal Communications Commission could require Gannett to sell some stations or newspapers it owns because of rules restricting multiple media outlets in the same market. The companies said only five markets are potentially affected — Phoenix, St. Louis, Portland/Salem, Ore., Louisville, Ky., Tucson, Ariz.

The deal transforms Gannett from “a newspaper company with broadcast and digital assets to being a broadcast company with strong newspaper and digital assets,” said Ken Doctor, a media analyst with Outsell Inc.

Shares of both companies soared to their highest prices since 2008.

Gannett President and CEO Gracia Martore called the acquisition an “important step” in the company’s diversification and said it will significantly improve the company’s cash flow and financial strength.

The acquisition will make Gannett, based in McLean, Va., one of the country’s largest owners of major network affiliates, reaching nearly one-third of U.S. households. It nearly doubles Gannett’s portfolio from 23 to 43 stations and gives it 21 stations in the country’s top 25 television markets.

Gannett expects the deal to boost its adjusted earnings by 50 cents per share within the first 12 months and generate $175 million in annual cost savings within three years after closing.

The deal, which has been approved by the boards of both companies, is expected to close by the end of 2013. It needs approval from the FCC and at least two-thirds of Belo shareholders.

Belo executives and shareholders representing about 42 percent of the company’s voting power support the sale, the companies said.

The move should help stabilize Gannett at a time when the newspaper business is faltering. Last year, revenue at Gannett’s publishing business fell nearly 3 percent to $3.7 billion, compared with a year earlier. By contrast, broadcast revenue grew more than 25 percent to $906 million, much of it from political advertising.

In recent months, Gannett’s newspapers have turned to a new revenue source: charging readers fees to access many of its websites. Because of that, revenue in the publishing division was mostly unchanged at $871 million in the first three months of the year.

Broadcast revenue during the same period grew nearly 9 percent to $192 million, even without major political campaigns.

In the latest quarter, earnings increased 53 percent to $105 million, boosted by a tax benefit and the new website fees. The company’s revenue was up less than 2 percent, meeting Wall Street’s expectations.

Doctor said the deal will give Gannett more negotiating clout over fees that local TV stations get from cable and satellite TV companies for the right to include those stations on cable and satellite systems.

“The pressures on profit in the newspaper sector are much greater than in the broadcast sector,” the analyst said.